<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>背景属性</title>
    <style>
        .one{
            width: 400px;
            height: 400px;
            background: rgba(0);
            border: blue solid 50px;

        }
        .two{
            width: 400px;
            height: 400px;
            background-color: red;
            border:blue solid 50px;
        }
    </style>
</head>
<body>
    <div class = "one"></div>
    <div class = "two"></div>
    
</body>
</html>